San Francisco Bay – Gray whales, massive migrants from Arctic feeding grounds to Mexican breeding areas, have increasingly ventured into the busy waterway in recent years. Researchers attribute this shift to dwindling prey in their traditional habitats, disrupted by warming oceans.[1][2] Once rare visitors, these 40-foot giants now encounter heavy ship traffic, leading to a troubling spike in fatalities. A new study reveals the bay’s hidden dangers for the struggling population.
A Surge in Sightings Signals Trouble
Scientists cataloged 114 unique gray whales in San Francisco Bay between 2018 and 2025 through photo-identification efforts.[3] Most came from the Eastern North Pacific stock, with few matching known foraging subgroups like the Pacific Coast Feeding Group. Only four whales returned across years, hinting at low survival rates. Surveys involved vessel outings, community photos, and matching markings on flanks, dorsals, and flukes.
Whales lingered for weeks on average – 27 days in 2023, 24 in 2025 – far longer than typical coastal passes. This pattern emerged around 2018, echoing rare stops in the late 1990s during past food shortages. Lead researcher Josephine Slaathaug noted the change: “It was historically very unusual for them to enter the bay, especially for longer amounts of time or consistently year after year.”[4]
Vessel Strikes Emerge as Primary Killer
Of the 114 identified whales, 21 matched to carcasses, establishing a minimum mortality rate of 18 percent.[3] In the broader region, 70 gray whale carcasses turned up, with 30 – or 43 percent – showing blunt or sharp force trauma consistent with ship collisions. Among matched deaths with determined causes, nine of 11 traced to vessel strikes. Slaathaug emphasized: “It’s really important to understand that these are just minimums that we were fully able to confirm.”[1]
Thirteen matched carcasses washed up inside the bay itself. Experts suspect the true toll nears 40 to 50 percent, as skin decay and unrecovered bodies limit matches. “What is unique about San Francisco Bay and this study was that there was such a clear emerging cause of death,” Slaathaug added.[4] Malnutrition weakened many victims, compounding strike risks.
Climate Change Disrupts Ancient Migration
Gray whales travel over 10,000 miles annually, foraging on amphipods in the Bering and Chukchi seas during summer. Ocean warming has cut sea ice, degraded sediment habitats, and slashed prey quality, driving a 50 percent population drop since 2016.[2][4] Now numbering around 13,000, the Eastern North Pacific stock seeks alternatives like San Francisco Bay…